Solid state electronic devices are typically encapsulated in plastic via transfer molding. Encapsulation protects the device from environmental and mechanical damage and electrically isolates the device. There are many desired technical features of encapsulant compositions. Encapsulation of wire-bonded devices requires low viscosity encapsulant injection, followed by rapid cure and hot ejection. In order to avoid damaging the solid state device, the encapsulant must not shrink excessively on curing. The encapsulated device must subsequently withstand the rigor of solder assembly onto a circuit card. The encapsulant must also be self-extinguishing in the event of a heat-producing malfunction of the circuit. And the encapsulant must adhere strongly to copper leadframes.
In current epoxy-based encapsulation compositions, it is advantageous to use as much mineral filler as possible in order to decrease moisture absorption and thermal expansion of the cured composition. However, higher filler levels are associated with reduced flow and impaired moldability, which are manifested as poor mold filling and increased defect generation. There is therefore a need for encapsulation compositions that exhibit increased flow at high filler loadings.